名稱輸出顯示「null」Java

Question

我正在製作一個遊戲類型的事物與三個類組合。 不是家庭;愛好。

代碼爲三類：

亞軍：

public class CounterGameRunner 
    { 
    // instance variables - replace the example below with your own 
    public static void main(String [] args){ 
    Scanner input = new Scanner(System.in); 

    CounterGameCounter game = new CounterGameCounter(); 

    System.out.println("You want to play a game I see. What is your name?"); 

    String name = input.next(); 

    game.NameIn(name); 


    CounterGAME game1 = new CounterGAME(); 

    game1.actual(); 

} 
} 

實際遊戲：

public class CounterGAME 
{ 
    // instance variables - replace the example below with your own 

     Scanner input = new Scanner(System.in); 

     int number; 
     int count=1; 
     boolean loop = true; 
    public CounterGAME(){ 


    } 

    public void actual(){ 

     CounterGameCounter game2 = new CounterGameCounter(); 


     System.out.println("Guess a number between 1 and 101, see how many times you get it!"); 

     number=input.nextInt(); 
     int r = (int)(Math.random() * (100) + 1); 
     while(loop==true){ 


    if(number < r){ 
     System.out.println("Too small, try again"); 
     number = input.nextInt(); 
     count++; 
     game2.Counter(count); 

     } else if(number == r){ 
     System.out.println("Wow, you won! Who'd have thought?"); 
      count++; 
      game2.Counter(count); 
      break; 

    System.out.println(game2.done()); 

     } else if(number > r){ 
     System.out.println("Too large, try again"); 
      number = input.nextInt(); 

      count++; 

     game2.Counter(count); 
    } 


     } 





     } 



} 

Counter類：

public class CounterGameCounter 
    { 
     // instance variables - replace the example below with your own 



private String Name; 

String done1; 
int correct; 

public CounterGameCounter(){ 



} 



public String NameIn (String nm){ 
    Name = nm; 
    return Name; 
} 

public String NameOut(){ 

    return Name; 

} 


public void Counter(int count){ 

    correct = count; 

} 

public int getCount(){ 



    return correct; 

} 


public String done(){ 
    done1 = "Name: "   + NameOut() + "\n" + 
      "Times Answered: " + getCount(); 




    return done1; 
    } 



} 

問題：

計數器正常工作，並最終一切顯示和功能正常。但是，我在開始時輸入的任何名稱在運行程序時總是顯示「null」。爲什麼？

Answer 1

你的變量名是真正的混亂，有很多的代碼中的不良行爲，但null的名字是因爲你創建一個新的Counter在CounterGAME：

public void actual(){  
    // here 
    CounterGameCounter game2 = new CounterGameCounter(); 
    // more code 
} 

更改實際接收CounterGameCounter ：

public void actual(CounterGameCounter game2){ 
    // more code 
} 

，並調用它像：

public static void main(String [] args){ 
    Scanner input = new Scanner(System.in); 
    CounterGameCounter game = new CounterGameCounter(); 
    System.out.println("You want to play a game I see. What is your name?"); 
    String name = input.next(); 
    game.NameIn(name); 
    CounterGAME game1 = new CounterGAME();  
    game1.actual(game); 
    // more stuff 
} 

---

FREE TIPS：

• 使用String getName()和void setName(String)

• 開始變量，對象和屬性名與lowercase

  String name; 
  Object object; 
  

• 變量名必須是代表性和說明性的

  CounterGameCounter counterGameCounter = new CounterGameCounter(); 
  

  這也適用於Object名稱：

  GameCounter gameCounter = new CounterGameCounter(); 
  

Answer 2

試試這個：的

String name = input.nextLine(); 

代替：

String name = input.next();